I never have auras or strange smells or some of the other distinctive migraine
symptoms.

I've been having these headaches at irregular intervals (anywhere from every
few weeks to every couple of months) for at least 15 years. They don't seem
to correlate with any particular activity. I'm pretty sure dehydration,
especially from an airplane flight, triggered some of them in the past.
Sometimes I think eating an over-large meal may trigger them a bit.

Course of the headaches:

They often last 2 or 3 days, varying from low-grade to somewhat debilitating.

I take acetaminophen (Tylenol) and sinus allergy medicine. I haven't
tried any prescription migraine medicine, or any other remedies.

I try to drink a lot of water, to make sure I'm not dehydrated.
Sometimes it eases the sinus pain briefly.

My father had high blood pressure, Parkinson's, and maybe a couple
of small TIAs just before he died around age 70. He also had smoked heavily earlier in life and
had a couple of bouts of cancer as a result.

I've never smoked, or used any illegal drugs (how many people can say
that these days ?).

I've always been a very moderate drinker; one drink every two days is
about as heavy as I ever get.

My caffeine intake is a glass of iced tea at lunch, and a Diet-Coke mixer
with my alcohol every couple of days.

My father had "hay fever" allergies, with a lot of sneezing and eye-watering,
but I've never had anything like that.

I could stand to lose 20 pounds, but feel I'm in decent shape for age 49.

I thought eyestrain might be causing the headaches (I do a lot of reading
and computer use), but an eye exam and new glasses (bifocals) haven't
stopped the headaches.

I thought teeth-grinding at night (bruxism) might be causing the headaches,
but my dentist apparently didn't see any tooth damage. I bought a night-guard
and used it for a couple of weeks, but it was so uncomfortable that I stopped using it.

Turns out I have more family history of migraines than I remembered:
my mother's mother had them, and one of my sisters has them.

Relief:
I've found that taking Tylenol (acetaminophen) and ibuprofen simultaneously
often knocks out my headaches; either by itself is not enough. A shot
of caffeine (iced tea) along with the pills helps too.

More relief:
Taking migriane medicine works !
I've had success with Imigran (sumatriptan), and
Tonopan (caffeine, propyphenazone and dihydroergotamine mesylate).
I take one or the other; never both.

Bought a bottle of sumatriptan from a UK pharmacy over the internet
(no prescription needed). It actually shipped from Vanuatu, for some reason.

But now when I have a headache, I don't know if I should take "normal"
medicine such as acetaminophen, or migraine medicine such as sumatriptan.
Usually turns out to be a migraine.

Bought a home blood-pressure tester
(on Amazon),
and my blood-pressure seems to be fine.